Carbon monosulfide generating process

ABSTRACT

This application concerns a process for generating carbon monosulfide (CS) in quantity for a carbon monoxide (CO) chemical laser using thermochemical dissociation of carbon disufide (CS 2 ) in a high temperature (T≧ 2400 K) fuel-oxidizer flame.

BACKGROUND OF THE INVENTION

Recent advances in the development of a carbon monoxide (CO) chainreaction chemical laser capable of high cw power output have created theneed for an efficient method of generating large quantities of CS. Inthe CS fueled CO chemical laser, molecular oxygen (O₂) in combinationwith CS, produces a chemical chain reaction which results in theproduction of vibrationally excited CO. The CS molecule is stable in thegas phase; however, a heterogeneous process involving the recombinationof CS to produce CS₂ on contact with a wall precludes accumulation andstorage of large quantities of CS. Any practical large scale CS fueledCO chemical laser requires a CS generator as an integral component.

Present devices for producing CS rely on electrical power. These devicesare inefficient and would be impractical for large scale lasers.

The most practical method of producing CS for CO chemical laserapplications is by the thermal dissociation of CS₂. If the energy forthe dissociation is provided by a thermochemical combustion process,large quantities of CS can be produced from a combustor unrestricted insize. However, additional chemical species generated by thethermochemical combustion process must not interfere with either thechemistry of the CO laser or cause significant degradation of opticalgain produced in the CO laser.

Accordingly, a principal object of this invention is to provide athermochemical combustor using a fuel-oxidizer flame and CS₂ to generateCS, the energy for the dissociation of CS₂ being provided by the highenergy release of the flame. More specifically, an object of thisinvention is to provide a cyanogen (C₂ N₂)--O₂ flame to thermallydissociate CS₂ to provide a source of CS fuel for a CO chemical laser.

In copending application of Jeffers et al Ser. No. 473,695 filed May 28,1974 (now abandoned in favor of Continuation application Ser. No.648,273), is disclosed a process and apparatus for a CO chemical laserCS-CS₂ fuel in which the CS is generated by DC glow discharges. Thesedischarges provide CS/CS₂ in molar ratios from 0.3 to a practical levelof 0.5. In copending application of Jeffers and Ageno Ser. No. 658,497entitled CO Chain Reaction Chemical Laser is disclosed a chain reactionCO chemical laser using CS fuel. The present application provides amethod of making substantial amounts of CS to use as fuel in theprocesses of said copending applications.

DESCRIPTION OF THE DRAWINGS

The FIGURE is a schematic representation of the apparatus used toproduce CS in this invention.

DETAILED DESCRIPTION

In order to dissociate CS₂ and produce CS, a temperature of 2400 K orgreater is necessary. A number of fuel-oxidizer-CS₂ gas mixtures producethe necessary adiabatic flame temperatures as well as satisfactorychemical equilibrium compositions. The fuel oxidizer mix chosen fordemonstration is C₂ N₂ --O₂. Other suitable combinations include C₂ N₂--NF₃ ; C₂ H₂ --NF₃ ; Al/NF₃ ; N₂ H₄ --NF₃ ; N₂ H₄ --F₂ ; NH₃ --NF₃ ; H₂--ClF₃ ; H₂ --NF₃ ; CH₄ --NF₃ ; and C₃ H₈ --NF₃.

In addition to providing a sufficiently high temperature, thefuel-oxidizer-CS₂ system must be designed to generate as by-productsonly gases which do not adversely affect the laser operation of the COchemical laser for which the CS is generated as fuel. The fuel oxidizersof the foregoing list meet both of these criteria.

This disclosure specifically concerns a C₂ N₂ --O₂ fuel-oxidizer system,but is equally applicable to the other fuel-oxidizer systems listed.

Critical features of this system are the CS mole fraction and the CS/CS₂ratio.

Since CS₂ acts as a chain terminator in the CO chemical laser chainreaction, CS/CS₂ ratios greater than 2 are necessary for a practicaldevice. Reactant CS₂ molar fractions of less than 33% produce CS/CS₂ratios greater than 2.

Another variable is the concentration of C₂ N₂ in the gas mixture. A C₂N₂ lean gas mixture yields unacceptably low CS concentrations. For theC₂ N₂ rich flame, i.e., where C₂ N₂ /O₂ is about 1.2, larger CSconcentrations and higher CS/CS₂ ratios are obtained at a lowertemperature with less CS₂ reactant than for flames using stoichiometricamounts of C₂ N₂ and O₂. A minimum C₂ N₂ /O₂ ratio is about 1.0. Amaximum C₂ N₂ /O₂ ratio is about 1.3.

Carbon from the excess C₂ N₂ apparently combines with the sulfur derivedfrom the decomposition of CS₂ to produce CS, because there is a decreasein S₂ and S for the C₂ N₂ rich versus the stoichiometric gas mixture.The optimum operating conditions for the C₂ N₂ -O₂ combustor weredetermined to be a C₂ N₂ /O₂ ratio of about 1.2 with about 0.2 molarfraction of CS₂ reactant. Mixtures much richer than C₂ N₂ /O₂ of about1.2 produced large quantities of solid carbon.

The FIGURE shows a C₂ N₂ -O₂ -CS₂ combustor which was constructed andused in producing CS and which was used to extract CS from the hightemperature combustor plenum.

The combustor 10 is fabricated from 304 stainless steel and consists ofa water-cooled plenum 11, a supersonic nozzle 12, an injector head 13and an injector head plug 14. In the device used in this application,the plenum 11 dimensions are 1.0 cm i.d. by 1.5 cm long. The diameter ofthe nozzle throat 15 is 0.13 cm with a 19 to 1 area expansion ratio toproduce a Mach 4 supersonic exit flow. The supersonic expansion (Machflow greater than 1) is used to freeze the chemistry of the gas flow asmuch as possible and to reduce the static exit pressure to a levelsuitable for the mass spectrometer sampling probe 16. The Mach numbernormally is the range M= about 2 to about 5. The injector head 13contains a small mixing chamber 17 where the CS₂ flow mixes with the C₂N₂ /O₂ flow. A premixed gas feed system was chosen to insure a rapidapproach to equilibrium in the combustor plenum 11. The injector headplug 14 contains a sintered metal filter which acts as a flashbackarrestor and pressure snubber. The gas is injected into the plenumthrough four 0.089 cm diametr orifices 18.

The C₂ N₂ was technical grade, 98.5% and the O₂ was extra dry grade,99.6%, and both were used directly from their bottles without furtherpurification. The CS₂ was reagent grade and was degassed before use. Inorder to achieve an adequate supply pressure for the CS₂, the bottle andsupply lines were contained in a heating jacket and maintained at 100°C. The vacuum in the test cell was about 0.1 Torr.

The concentrations of CS, CO, N₂, and CS₂ were measured by the massspectrometer sampling probe 16.

In operating the combustor device 10, the combustor flame was ignited byflowing all three gases (C₂ N₂ -O₂ -CS₂) premixed into the plenum 11 andsparking the ignitor wire with a Tesla coil. Wall temperatures of 680°C. and 410° C. were measured by thermocouples for the downstream andupstream ends of the plenum, respectively. Mass flow measurements wereconsidered accurate to ±2% for the C₂ N₂ and O₂ flows and to ±10% forthe CS₂ flow. For typical operating conditions the temperature in theplenum 11 was 2750 ≅ 500 K. This temperature was consistent withcalibrated adiabatic flame temperatures and estimated heat losses due toconduction from the hot plenum walls to the cool test cell flange. Heatloss based on the observed plenum wall upstream and downstreamtemperatures and one dimensional heat conduction was calculated to beapproximately 30 W. This typically represents a 10% loss of theavailable flow energy based on calculated adiabatic flame temperatureand measured mass flow rates.

For input combustor flow of C₂ N₂ = 1130 sccm, O₂ = 1000 sccm, and CS₂ =305 sccm, the principal end products for these optimum flame conditionsas measured by the mass spectrometer 16 are CO, N₂, CS and CS₂. MaximumCS/CS₂ ratios of 4 were observed and 20- 30 weight percent of the exitstream is CS. Under stoichiometric C₂ N₂ --O₂ conditions, the observedmass scan confirms the expected presence of S₂ and diminished CSconcentration. Finally, increasing O₂ sufficiently to oxidize the CS₂results in the principal products of the CS₂ -O₂ flame being SO₂ and CO.The chain reaction for CS₂ -O₂ is completely independent of the C₂ N₂-O₂ chain.

What we claim is:
 1. A method of producing CS as an entity comprisingthe steps of heating CS₂ with a fuel-oxidizer flame in a systemcontaining a fuel, an oxidizer and CS₂ to a temperature of at least 2400K to produce a mixture of CS and CS₂, recovering the mixture from thesystem in a form in which the ratio of CS/CS₂ is at least 2 by passingthe gases produced by the system through a nozzle in a supersonicexpansion thereby to preserve the CS as an entity in the mixture for apredetermined period of time by means of said supersonic expansion, andemploying said mixture to utilize said CS entity within saidpredetermined period of time.
 2. The method of claim 1 wherein thefuel-oxidizer system is C₂ N₂ --O₂.
 3. The method of claim 2 wherein theC₂ N₂ /O₂ ratio is more than about 1.0 and less than about 1.3.
 4. Themethod of claim 1 wherein the molar fraction of the reactant CS₂ is lessthan about 33 molar percent in the input.
 5. The method of claim 1wherein the molar fraction of the reactant CS₂ is about 0.1- 0.2.
 6. Themethod of claim 1 wherein the fuel-oxidizer system is C₂ N₂ -O₂ and theratio of C₂ N₂ /O₂ is about 1.1.
 7. The method of claim 1 wherein thesupersonic expansion flow is Mach 2 or more.